Although our heads are full of simple, selfish biases that evolved to help our ancestors survive, modern human beings are anything but simple and selfish cavemen, argues social psychologist Douglas Kenrick. Many of our ingrained, apparently irrational behaviors—including one-night stands, prejudices, and conspicuous consumption—ultimately manifest what Kenrick calls "Deep Rationality," and form the basis of more complex feelings, including generosity, creativity, and love. Using his own experiences as a husband, father, doctor, and former juvenile delinquent as a point of departure, Kenrick explores the hidden value of our dark side.